Open MPI will not require a full set of daemons like LAM/MPI does. You
can have a full set if you wish, especially in environments where it
makes sense (e.g., rsh/ssh, where there is little other infrastructure
to do proper distributed process control). There will be helper
commands analogous to lamboot/lamhalt to help launch/kill these
daemons.

For other environments, you can simply mpirun directly. Unlike LAM,
mpirun has the capability to talk to PBS (for example), rather than
lamboot.

> 1) Is Open MPI thread-safe (assuming the system-supplied libraries are
> thread-safe)? In particular will it be possible to call MPI routines
> from OpenMP regions and will it be possible to use OpenMP directives
> within MPI tasks?
>
> 2) Does Open MPI use the same mechanism as LAM-MPI's "lamboot"
> (rsh/ssh) to start daemons on other nodes or is there a different
> mechanism altogether?